Heavy work vehicles are known, used in the building trade, normally consisting of a truck on which an extendable and/or telescopically extending arm is assembled, articulated for dispensing and casting concrete. The trucks may or may not be equipped with a concrete mixer.
Extendable arms of the known type consist of a plurality of segments hinged to each other and which can be folded back one on the other, so as to be able to assume a folded configuration close to the truck, and work configurations which can reach areas which are even very far from the truck.
One of the most important features of these extendable arms is the capacity to reach the greatest heights and/or lengths possible, so as to be able to guarantee maximum flexibility and versatility with the same truck.
An increase in the number of articulated segments, or an extension of the length of each of them, on the one hand allows to obtain greater overall lengths when at maximum extension but on the other hand causes an increase in weight and bulk which is not compatible either with current legislation or the effectiveness and functionality of the vehicle.
It is also known that a shortcoming which is often complained about with regard to the correct effectiveness of these arms is the phenomenon of vibrations to which the arm is subjected while it is delivering concrete: the greater the overall length of the arm and the number of segments, the more this problem is felt. These vibrations cause considerable operating difficulties both for the operator who is responsible for the manual positioning and orientation of the exit tube of the concrete, and also for the operator moving the arm by remote control.
An important component of these vibrations also derives from the type of the machines and from their relative characteristics of slenderness, inertia and elasticity, as well as the constructive type. In fact, these characteristics induce dynamic stresses in the articulated arm, which are associated both with the modes of the machine itself, in a substantially static condition, or at least not pumping, and also with the dynamic loads associated with the concrete pumping step.
Indeed, in order to be used, the machine works by moving from one configuration of the arm to another: this implies that its own mode is continuously excited and dynamic variations are generated on the state of stress of the joints and in the material, which limits the working life of the machine and reduces safety for the workers.
Furthermore, to these effects are also added the forced and pulsed functioning associated with the piston pump used for pumping the concrete, which often happens at frequencies close to those of the machine itself.
A method to actively control the vibrations of an articulated arm for pumping concrete is described in EP 2103760 in the name of the present Applicant, which describes a method to contain the first vibration modes of the articulated arm, which are those that most determine the dynamic load and hence the onset of vibrations.
Documents JP 2057703 and JP 11101202 are known, that disclose controlling devices for hydraulic cylinders having actuators, which devices comprises sensors to detect the travel of the actuators, and a control unit to receive information from the sensors and to control the hydraulic pumping device of the hydraulic drive circuit at which the actuators are connected.
In particular, document JP 2057703 allows to reduce the shock, and so the vibrations, due to the stroke end of a hydraulic cylinder, reducing the speed at which the hydraulic cylinder expands/contracts when the cylinder is near the stroke end.
However, these devices have the drawback that they do not allow an active control of the vibrations but allow only to reduce the onset.
Moreover, they are concerned only with a factor that could generate the vibration of one segment of the arm, and not to the general problem of avoiding the presence of vibrations along the whole arm.
Purpose of the present invention is therefore to supply a device to actively control the vibrations of an articulated arm, which allows to correct and compensate the vibrations of the articulated arm.
The Applicant has devised, tested and embodied the present invention to obtain this purpose, and other advantages explained hereafter.